A sliding sleeve of the above type is known, for example, from DE 39 08 989 C2 and is formed by two symmetrical or almost symmetrical halves which are produced separately by a shaping procedure and then connected to each other by a joining process. Each symmetrical half comprises a disc-shaped, circumferential shoulder projecting radially outwards from its outer peripheral surface. After the joining of the two symmetrical halves, the end faces of the shoulders oriented towards the central transverse plane of the sliding sleeve, and the cylindrical surface defined between these shoulders on the outer peripheral surface together form the gearshift fork guide.
The inner peripheral surface of this sliding sleeve comprises a toothing whose teeth, as seen from the end face, taper in cross-section towards the central transverse plane so that central cavities are formed in the central transverse plane on the tooth flanks. These cavities assure that the teeth of the sliding sleeve and those of the dog-type toothing of the clutch body or of the gear wheel which mesh with each other when a gear has been selected cannot come disengaged from each other, particularly during load alternation. Besides the cavities on the tooth flanks, it is also possible to arrange, for example, recesses and grooves on or between the teeth of the internal toothing of sliding sleeves. Further, the ends of the teeth of sliding sleeves are often provided with roof slopes.
These recesses are engaged by the locking pins of the synchronizer assembly which are generally biased by a spring. This locks the sliding sleeve in its neutral position when no gear has been selected. The grooves which are aligned to the central longitudinal axis of the sliding sleeve serve, for example, to receive and guide thrust members of the synchronizer assembly. When the sliding sleeve is displaced in axial direction for selecting a gear, the thrust members press the synchronizer ring against the friction cone of the clutch body. The roof slopes of the teeth prevent the toothing of the sliding sleeve from locking prematurely into the toothing of the clutch body or of the gear wheel during synchronization. But when synchronization has been terminated, the roof slopes facilitate this locking.
There are other types of sliding sleeves which, in addition to the toothing on the inner peripheral surface, also possess a toothing on the outer peripheral surface of the sleeve body. This external toothing is engaged, for example, by a sliding intermediate gear wheel of the reverse gear in so-called compact transmissions when the sliding sleeve is situated in a position of shift between the first and the second gear of a manual transmission.
It is known that the cost of production of the sliding sleeve can be reduced compared to machining methods by the use of non-chipping procedures. In the state of the art, it is not possible to produce the aforesaid profiles viz., cavities, recesses, grooves and roof slopes, in one-piece sliding sleeves exclusively by non-chipping shaping. This is the case because the contours of these recesses overlap. For example, the contours of a drawing die or project beyond them and thus form undercuts in the direction of die removal.
For producing sliding sleeves exclusively by non-chipping methods, these undercuts have been avoided thus far as described in the example of DE 39 08 989 C2 by making the sleeve body of the sliding sleeve in two separate parts which are then joined together. The joining plane of these two parts extends through the plane of separation of the cavities so that no undercuts are formed in the direction of removal, for example, of a drawing die. In this example, the joining plane corresponds also to the plane of symmetry of the sliding sleeve because the two parts of the sleeve which are joined together have a symmetrical or almost symmetrical configuration.
There are also sliding sleeves in which the recesses on the inner diameter for receiving the locking pins and/or the grooves for guiding the thrust members are arranged in the central transverse plane, and the cavities are disposed between the central transverse plane and the end faces of the sliding sleeve in the tooth flanks. It is also possible to provide both a groove or a recess as well as a cavity on the flanks of one and the same tooth. If these prior art sliding sleeves are to be produced exclusively by non-chipping methods, undercuts can only be avoided by providing more than two joining planes so that the sleeve body must be made of more than two separate parts. The drawback of this is that, with an increasing number of individual components of a sliding sleeve, the equipment and production costs are also increased. The joining of the sleeve components leads to the addition of the dimensional and shape deviations arising from the joint to the already existing dimensional and shape deviations of the recesses, cavities and grooves. This detracts from the precision of the finished sliding sleeve.
If it is not possible to make the sleeve body by joining several parts together, the recesses have to be made by an additional work step of machining. This leads to additional processing and handling costs which increase the cost of manufacture of the sliding sleeve.
In DE 39 08 989 C2, a circumferential shoulder is arranged on the outer peripheral surface of each symmetrical half of the sliding sleeve. When the two halves are joined together, the opposing end faces of these shoulders and the part of the outer peripheral surface of the sleeve body enclosed between them form a circumferential groove, that is to say, the gearshift fork guide, into which a gearshift fork of the manual transmission engages. These shoulders constitute stops through which the axial displacement is transmitted by the gearshift fork to the sliding sleeve. The joining plane formed by the joining of the symmetrical halves also forms the central transverse plane of the sliding sleeve and thus also the central transverse plane of the gearshift fork guide. Consequently, the dimensional and shape deviations of the joint are added to the dimensional and shape deviations of the gearshift fork guide. In this case too, the joint therefore detracts from the precision of the sliding sleeve.